Fix dtrace and inhibit_all_warnings!

This modification fixes CocoaPods/CocoaPods#1510, also brought up in ReactiveCocoa/ReactiveCocoa#866 and Cocoapods/Specs#4620.

Known issues:
- no compiler flags are passed to dtrace, ever. this is probably okay.
- no spec tests this
- it duplicates a little bit of work. i didn't want to neaten it up, so that you guys could see still the structure. i'll happily extract the variable and save some cycles if you like.